This invention relates to an improvement in free-wheeling hub assemblies for four-wheel drive vehicles. More particularly, it relates to an improvement in venting a diaphragm chamber to atmosphere such that the position of the diaphragm can be accurately controlled.
Modern four-wheel drive vehicles have a pair of free-wheeling hub assemblies for selectively driving all four vehicle wheels. In some free-wheeling hub assemblies, the connection of a drive shaft to the hub assembly to drive the hub assembly is controlled by a diaphragm. A hydraulic chamber positions the diaphragm in order to engage and disengage the hub assembly from the drive shaft in response to commands to selectively drive the associated wheels. A free-wheeling hub assembly is disclosed in U.S. Pat. No. 4,625,846 to Gomez and is assigned to the assignee of the present invention. This patent is expressly incorporated by reference and will fully explain and disclose the operation of the free-wheeling hub assembly of this invention.
In a prior art free wheeling hub assembly, an external body is connected to rotate with a wheel hub. A cylindrical axle hub is received within the external body and has internal splines that are received in external splines formed on the axle shaft. Snap rings secure a bearing to the outer periphery of the cylindrical axle hub. The wheel hub and axle shaft may rotate relative to each other upon this bearing, while the vehicle is in two-wheel-drive mode.
The wheel hub will typically receive a rim and tire and is one of the selectively driven wheels of a four-wheel drive vehicle. The operator of the vehicle may selectively engage the two wheels that have the free-wheeling hub assemblies to provide four-wheel drive to the vehicle.
An external toothed section on the cylindrical axle hub is associated with internal teeth on a clutch ring. The clutch ring has locking teeth that are received within slots or grooves in the inner periphery of the external body to rotate the external body along with the clutch ring when it is driven to rotate by the axle hub. Due to the teeth on the clutch ring it can slide longitudinally within the external body. The clutch ring can also slide on the externally toothed section of the axle hub.
Radial projections connect an actuating disc to the clutch ring and a central rivet connects a diaphragm to the actuating disc. A disc or backing member receives the central rivet and prevents the diaphragm from being torn. In addition, the disc has a cylindrically upstanding portion that will abut an end wall of the external housing and prevent excess deformation of the diaphragm. The upstanding portion is a stop means for the diaphragm. A spindle receives the axle shaft within its inner periphery and the wheel hub outside its outer periphery. The spindle is fixed to the vehicle frame. An oil seal seals the end of the spindle from atmosphere. A radially extending flange is formed extending from the spindle outwardly. A seal is received between the spindle and wheel hub. A bearing is received within the spindle and supports the axle.
Fluid, which may be hydraulic pressure, air or vacuum pressure is communicated to a control pressure chamber in one of two ways. In one embodiment, a tube is received in an orifice formed in the spindle. The tube is communicated to a canal or passage which communicates with a radial spacing between the axle shaft and the inner periphery of the spindle. From this radial spacing, fluid is communicated into the chamber to control the pressure within the chamber.
Alternatively, a passage is formed within the inner periphery of the axle shaft and communicates the fluid to the chamber through the axle shaft.
A vent opening is formed in the end wall of the external housing and will allow venting of the pressure within a diaphragm chamber. A powdered metal filter is received within the vent opening.
A spring will bias the diaphragm to a position in opposition to the pressure with the control pressure chamber. If a high pressure fluid is sent to the control pressure chamber, the spring will bias the diaphragm away from the end wall. If a vacuum pressure is utilized, the spring will bias the diaphragm toward the end wall.
The basic operation of this prior art device will be explained. When it is desired for the wheel hub to not be driven, pressure fluid may be communicated to the control pressure chamber thus biasing the diaphragm in the direction of the wall. The clutch ring will slide along therewith and internal teeth will be removed from the externally tooth section of the cylindrical axle hub. Even though the axle shaft is being driven, this drive will not be transmitted through to the clutch ring, the external body and through to the wheel hub since the internal teeth are not received upon the externally toothed section of the cylindrical axle hub.
When it is desired to drive the wheel hub, the pressure in orifice will be removed, or alternatively a vacuum will be applied to this passage. The direction of the spring bias will depend on whether high-pressure of vacuum pressure is sent to the control pressure chamber. This will draw the diaphragm in a direction away from the wall and will cause the clutch ring to slide along therewith. The clutch ring internal teeth will now align with the external tooth section of the cylindrical axle hub. Drive will be transmitted from the axle shaft through to the clutch ring which in turn will drive the external body through the teeth. The wheel hub is thus driven to rotate.
In this type of free-wheeling hub assembly, the relative pressure between the diaphragm chamber and the pressure chamber controls the position of the diaphragm. The pressure in the diaphragm chamber resists movement of the diaphragm in the direction of the wall. Thus, the pressure in the diaphragm chamber must be considered in conjunction with the strength of the spring biasing the diaphragm either towards or away from the wall and the pressure that is communicated to the control pressure chamber. If the pressure in the diaphragm chamber is greater than estimated, the clutch ring could be engaged when it is not desired. Alternatively, a lower than estimated pressure could cause the clutch ring to not engage or only partially engage when four-wheel drive is desired. If this relative pressure between the two chambers is not accurately monitored, it is difficult to control the position of the clutch ring.
The relative pressure between the pressure chamber and the diaphragm chamber can vary greatly, due to the elevation or temperature variation. For this reason, the prior art has vented the diaphragm chamber to atmosphere in an attempt to accurately control the pressure within the chamber. A vent opening with a powdered metal filter received therein is disposed in the wall. This vent communicates the diaphragm chamber to atmosphere in order to equalize their respective pressures. This connection of the diaphragm chamber to atmospheric pressure eliminates any extreme fluctuations in the relative pressure between the two chambers, which could affect the positioning of the clutch ring.
Problems sometimes arise with this type of prior art device since the filter can easily become clogged and prevent venting of the chamber. A free-wheeling hub assembly mounts a wheel and is quite close to the ground. The filter can easily become clogged with dirt. This filter is exposed to all kinds of impurities, especially in four-wheeled driving, which often occurs off paved roadways. When the filter plugs up, the chamber is sealed as if there was no vent at all. In addition, when the wheel hub is submerged water may be sucked into the chamber through the filter. This can render the mechanism inoperable and may damage the delicate components, and in particular the diaphragm. A filter in this location does not allow for easy maintenance and cleaning and may easily be clogged by paint, polishing wax or any similar products that may be applied to the vehicle. A powdered metal filter will tend to have some water in it due to moisture in the atmosphere and in colder temperatures, this water could freeze and clog the filter.
For this reason, it is an object of the present invention to disclose an improved vent for the diaphragm chamber of a free-wheeling hub assembly in which the chamber is vented to a clean area without contaminants or impurities.
More particularly, it is an object of the present invention to disclose an improved vent for a free-wheeling hub assembly in which the chamber is vented to a clean area inside the engine compartment of the vehicle.